Loud speaker



-zu/g INVENTOR WMA/55555. @ggf/2 y Sep. 20, 1932. Q HIGH 1,877,868

LOUD SPEAKER Filed March 2, 1951 ff BY l v ATTO'RNEY Patent'ednsept. 20, 1,932

UNITED STATES PATENT oFFlcE" J URJ' EN S. HIGH, 0F AKLYN MANOR, NEW JERSEY, ABSGNOR TO WESTINGBOUSE ELEC- ,y

TRIO & MANUFACTURING COMPANY, A CORPORATION 0l' PENNSYLVANIA LOUD SPEAKER Application led Iarchv 2, 1981. Serial No. 519,408.

My invention relates to telephonie instruments of the electrostatic type for transmitp tin or receiving purposes. More particular y, my invention relates to improvements in electrostatic microphones or receivers, particularly in a diaphragm of novel type where- .by results more nearly approaching the ideal condition of program reproduction may be obtained.

An electrostatic sound translator, as known to the prior art, comprises a fixed or relatively rigid conductive plate and a flexible resilient diaphragm spaced therefrom, but in relatively close proximity thereto. If an electric potential be impressed between the fixed and the movable members, an electrostatic force will develop between the two, and the movable member will be attracted toward the xed member.

Variation in the potential, such as may be caused by an audio-frequency potential be,- tween the two members, will produce corresponding vibratory motion of the diaphragm, whereby the alternating current is translated into sound waves.

Speakers of the electrostatic type are well known as possessing, inherently, more faithful reproducing characteristics than speakers of the magnetic or electrodynamic type. Perhaps the principal reason for this advantage is the fact that the diaphragm, as employed in speakers of the electrostatic type, need not be heavy and rigid. In fact, thediaphragm may preferably'consist of a relatively large thin sheet of metal, as, for example, metallic foil, in which case the diaphragm will comprise practically an inertialess member the fundamental period of vibration of which` phragm, over a drum-head structure in close lroxnnity to a iix'ed conducting perforated plate. Light fabric material, such as #3118 Japan sil would be very suitable for the purpose.'

A diaphragm structure, as described above, however, might offer mechanical diiculties in the construction and operation of the device. 'These diiculties would arise by reason of the fact that the diaphragm must be tensioned and maintained in that tensioned condition permanently. Since the metal coating normally has less tensile compliance than the fabric, there will be a tendency for it to break down, by cracking or tearing, during the operation f tensioning the phragmand also while being maintained under tension, by reason of temperature changes to whichl the diaphragm may be subjected.

It is, accordingly, one object of my invention to provide a diaphragm of the type referred to wherein tensile stresses in the conducting member are reduced to a degree where they are practically `eliminated.

' Another object of my invention is to provide a relatively strong and durable diaphragm which shall be substantially inertialess and of inappreciable weight.

Another object of my invention is to provide a diaphragm which will be rattle-proof in operation. l

Another object of my invention is to provide a speaker embodying a diaphragm of the type referred to whereby space requirements may be reduced and a high degree of sensitivity may thus be obtained.

In the accompanying drawing, I have illustratedy a loud speaker or microphone of the electrostatic type, embodying my invention.

Figure 1 of the drawing is a front elevational view of the speaker, and' Fig. 2 is a side elevationalview partly in cross section.

Fig. 3 is a view in cross section taken along the line III- III of Fig-1, Fig. 3 being a magniied view showing the details of construction. f

al1 the figures.

According to the manner in which I practice my invention, l provide a stationary electrode 1 comprising a rigid conductive plate having vents 3 throughout its surface for the emission of sound waves. ln electrostatic relationship thereto, I support my improved diaphragm 5, the supporting means 7 therefor being capable of cooperating with the stationary electrode, whereby the diaphragm may be tensioned to any desired degree.

.ln the particular modifications shown, the stationary electrode 1 is provided with a plurality of concentric arcuate surfaces 9 between which are provided elongated perforations 3 for providing the outlets for the sound waves produced by vibration of the diaphragm 5. A shoulder 11, in the form of a circular ridge, is provided on that surface of the stationary electrode 1 facing the diaphragm. rlhe function of this shoulder is to act, in cooperation with the diaphragm support 7, as a tensioning means for` the dia-- phragm 5, as will be more clearly explained 4 subsequently.

Thediaghragm, according to my invention, comprises a thin sheet of metallic foil 13 of aluminum or the like mounted in slidable engagement between a plurality of sheets of stretchable insulating material 15, such as fabric .or the like, a suitable example of which being the #3118 Japan silk referred to previously. This composite diaphragm is mounted upon the support 7 which comprises an element of substantially cylindrical shape,

- preferably provided with a depression in its outer cylindrical surface 17. The diaphragm 5 is loosely stretched upon one end of this element and maintained thereon by means of a thread or wire 19 wound around the cylindrical support -to force the overlapping edges of the diaphragm material into the depression 17 in the cylindrical surface of the supporting element. Thev diameter of the metallic-foil element 13 of the diaphragm is substantially less than the diameter of the supporting element 7 and, consequently, after the. diaphragm has been mounted upon its support, the metallic foil will possess substantial freedom of motion between the layers of the fabric material and, consequently, may be said to be in slidable engagement therewith.

In assembling the speaker elements, the diaphragm 5 is advanced toward the stationary electrode 1 until the shoulderll engages the loosely mounted diaphragm and creates a tension therein. The degree of tension may be regulated by means of adjusting bolts orA ment will remain substantially free from' stresses.

A. thin layer of varnish or other insulating material 25 will be applied to that surface of the stationary electrode facing the vdiaphragm to more safely insulate the diaphragm from the stationary-electrode.

The arcuate surfaces 9 provided in the sta- 85 tionary electrode l engage the diaphragm 5 f to increase the frictional contact Abetween the foil 13 and cloth 15, thereby preventing shifting of the metallic foil, which might normally be caused by reason of the vibration of the diaphragm.

If it were desired to employ a Hat surfaced stationary electrode in place of one having contacting arcuate surfaces, the diaphragm would have to be maintained in spaced relationship to the stationary electrode and, due to Vibration of the diaphragm, the foilr element might be caused to shift in position. This canI be prevented, however, by gluing the diaphragm to either one or both of the fabric sheets of materials at its central point. Since the tension stresses set up in the fabric sheets are in a radial direction, that is, from the center outward to the clamping points, no appreciable stretching will take place at 105 the center of the diaphragm. In other words, during the tensioning process, there will be substantially no relative movement between the insulating sheets and the metallic foil at the center of the foil element, and, 110 v consequently, the conductive element may be glued or otherwise attached to the fabric at this point without forfeiting the results'tobe obtained through the practiceof my invention.

Connections to both the stationary plate 1 andthe diaphragm 5 may be made as clearly illustrated in the drawing, the connection to the diaphragm passing through an insulating busiing 27 mounted on the stationary elec- 120 tro e.

By providing a composite diaphragm, as described, I' have obtained a vibratory element ofext-reme lightness, in addition to possessing great strength and durability. The 125 diaphragm is a1so-rattleproof by reason of the untensioned metallic foil and the teny sionedfabric supporting the-foil element in a rigid manner.

This will permit the use of unannealed foil which hasbetter tension L39 qualities than that of the annealed material Which is customarily employed. The arcuate surfaces 9 provided in the stationary electrode 1 permit the diaphragm 5 to be placed adjacent to it, thereby reducing the distance ordinarily required in structures of this type. Reduction in the spacing between the plate and the diaphragm results in an increase in sensitivity and response of the speaker.

I have, accordingly, described a loud speaker, of the electrostatic type, embodying a diaphragm which is capable of fuliillingthe objects of my invention. Various changes in the structure may be made Within the scope of my invention, and, therefore, I do not desire to be limited to the specific details disclosed except insofar as is necessitated by the prior art and the appended claim.

I claim as my invention:

An energy translating device comprising a support, a diaphragm mounted on said support, said diaphragm comprising a plurality of layers of substantially insulating material under tension and a layer of conductive material frictionally supported between certain layers of said insulating material, and means for securingsaid conductive layer to one of said insulating layers at its center only.

In testimony whereof, I have hereunto subscribed my name this 13th day of February,

JURJEN S. HIGH. 

